Photomultiplier

Abstract: A photomultiplier which can be easily made compact has a dynode unit (60) constituted by stacking a plurality of stages of dynode plates (6) in an electron incident direction in a vacuum container constituted by a housing (1) and a base member (4) integrally formed with the housing. Each dynode plate has an engaging member (9) engaged with a connecting pin (11) for applying a voltage at a side surface thereof. Through holes for guiding the connecting pins from the outside of the container are formed in the base member. Each engaging member is arranged not to overlap the remaining engaging members in the stacking direction of the dynode plates. The arrangement position of each engaging member and the arrangement position of the through hole for guiding the corresponding connecting pin to be connected are matched with each other.

Description: The present invention relates to an electron multiplier and to a photomultiplier. A conventional electron multiplier constitutes a photomultiplier having a photocathode. This electron multiplier is constituted by anodes and a dynode unit constituted by stacking a plurality of stages of dynodes in the incident direction of an electron flow in a vacuum container. Each dynode has a connecting portion for applying a predetermined voltage. The connecting portion and a stem pin connected to an external power supply terminal are electrically connected by a wiring member, thereby realizing the structure for applying a voltage to each dynode. In a broad sense the present invention can be said to be based in consideration of the arrangement of positions of connecting terminals for applying a voltage to plural dynode plates and a connecting pin (corresponding to the stem pin) for applying a voltage from an external power supply. The invention aims to make it unnecessary to use a wiring member whose length or shape can be freely changed, or three-dimensionally form the wiring member. Conventionally, when the wiring member is used, one end of this wiring member and the stem pin, and the other end of the wiring member and the connecting portion must be resistance-welded, respectively. This is a factor for decreasing the operation efficiency of assembling. As the photomultipliers to be manufactured become more compact, this decrease in the operation efficiency becomes more conspicuous. Since the welding operation requires skills, the operation efficiency of assembling is further decreased. The present invention aims to provide a photomultiplier having a structure which can facilitate the manufacture of even a compact photomultiplier. In an embodiment of the invention the engaging member is constituted by a pair of guide pieces for directly guiding the connecting pin. Therefore, even when the wiring member is connected, it is unnecessary to bend the end portion of this wiring member to reach the position where the engaging member is provided. According to one aspect of the invention there is provided an electron multiplier comprising: an anode plate; a dynode unit comprising a plurality of dynode plates so spaced apart from each other at predetermined intervals and so supported in the stack by way of insulating members that the last dynode plate of said dynode unit opposes said anode plate to enable the dynode unit to effect cascade-multiplying of electrons incident thereon; and a plurality of connecting pins, connected to respective dynode plates of the dynode unit to enable desired potentials to be applied to said dynode plates; characterised in that: said dynode plates each have an engaging member projecting from a predetermined portion of a side surface thereof to engage with a corresponding one of said connecting pins; and the positions of said predetermined portions of said dynode plates are so selected that said engaging members are at different positions and do not overlap each other along the direction of the stack of dynode plates in the dynode unit. According to another aspect of the invention there is provided a photomultiplier having an electron multiplier of the kind previously mentioned and further comprising a photocathode for receiving photons and emitting photoelectrons to said dynode unit. An embodiment of a photomultiplier embodying the present invention will be described in detail hereinbelow as comprising a photocathode and an electron multiplier including anodes and a dynode unit arranged between the anodes and the photocathode. The electron multiplier is mounted on a base member and arranged in a housing formed integral with the base member for fabricating a vacuum container. The photocathode is arranged inside the housing and deposited on the surface of a light receiving plate provided to the housing. At least one anode is supported by an anode plate and arranged between the dynode unit and the base member. The dynode unit is constituted by stacking a plurality of stages of dynode plates for respectively supporting at least one dynode for receiving and cascade-multiplying photoelectrons emitted from the photocathode in an incidence direction of the photoelectrons. The housing may have an inner wall thereof deposited a conductive metal for applying a predetermined voltage to the photocathode and rendered conductive by a predetermined conductive metal to equalize the potentials of the housing and the photocathode. The photomultiplier embodying the present invention has at least one focusing electrode between the dynode unit and the photocathode. The focusing electrode is supported by a focusing electrode plate. The focusing electrode plate is fixed on the electron incident side of the dynode unit through insulating members. The focusing electrode plate has holding springs and at least one contact terminal, all of which are integrally formed with this plate. The holding springs are in contact with the inner wall of the housing to hold the arrangement position of the dynode unit fixed on the focusing electrode plate through the insulating members. The contact terminal is in contact with the photocathode to equalize the potentials of the focusing electrodes and the photocathode. The contact terminal functions as a spring. A plurality of anodes may be provided to the anode plate, and electron passage holes through which secondary electrons pass are formed in the anode plate in correspondence with positions where the secondary electrons emitted from the last-stage of the dynode unit reach. Therefore, the photomultiplier has, between the anode plate and the base member, an inverting dynode plate for supporting at least one inverting dynode in parallel to the anode plate. The inverting dynode plate inverts the orbits of the secondary electrons passing through the anode plate toward the anodes. The diameter of the electron incident port (dynode unit side) of the electron passage hole formed in the anode plate is smaller than that of the electron exit port (inverting dynode plate side). The inverting dynode plate has, at positions opposing the anodes, a plurality of through holes for injecting a metal vapor to form a secondary electron emitting layer on the surface of each dynode of the dynode unit. On the other hand, the photomultiplier embodying the present invention may have, between the inverting dynode plate and the base member, a shield electrode plate for supporting at least one shield electrode in parallel to the inverting dynode plate. The shield electrode plate inverts the orbits of the secondary electrons passing through the anode plate toward the anodes. The shield electrode plate has a plurality of through holes for injecting a metal vapor to form at least a secondary electron emitting layer on the surface of each dynode of the dynode unit. In place of this shield electrode plate, a surface portion of the base member opposing the anode plate may be used as an electrode and substituted for the shield electrode plate. In particular, the electron multiplier comprises a dynode unit constituted by stacking a plurality of stages of dynode plates, the dynode plates spaced apart from each other at predetermined intervals through insulating members in an incidence direction of the electron flow, for respectively supporting at least one dynode for cascade-multiplying an incident electron flow, and an anode plate opposing the last-stage dynode plate of the dynode unit through insulating members. Each dynode plate has a first concave portion for arranging a first insulating member which is provided on the first main surface of the dynode plate and partially in contact with the first concave portion and a second concave portion for arranging a second insulating member which is provided on the second main surface of the dynode plate and partially in contact with the second concave portion (the second concave portion communicates with the first concave portion through a through hole). The first insulating member arranged on the first concave portion and the second insulating member arranged on the second concave portion are in contact with each other in the through hole. An interval between the contact portion between the first concave portion and the first insulating member and the contact portion between the second concave portion and the second insulating member is smaller than that between the first and second main surfaces of the dynode plate. The concave portion can be provided in the anode plate, the focusing plate, the inverting electrode plate and the shield electrode plate. The following points should be noted. The first point is that gaps are formed between the surface of the first insulating member and the main surface of the first concave portion and between the second insulating member and the main surface of the second concave portion, respectively, to prevent discharge between the dynode plates. The second point is that the central point of the first insulating member, the central point of the second insulating member, and the contact point between the first and second insulating members are aligned on the same line in the stacking direction of the dynode plates so that the intervals between the dynode plates can be sufficiently kept. Using spherical or circularly cylindrical bodies as the first and second insulating members, the photomultiplier can be easily manufactured. When circularly cylindrical bodies are used, the outer surfaces of these bodies are brought into contact with each other. The shape of an insulating member is not limited to this. For example, an insulating member having an elliptical or polygonal section can also be used as long as the object of the present invention can be achieved. In this electron multiplier, each dynode plate has an engaging member at a predetermined position of a side surface of the plate to engage with a corresponding connecting pin for applying a predetermined voltage. Therefore, the engaging member is projecting in a vertical direction to the incident direction of the photoelectrons. The engaging member is constituted by a pair of guide pieces for guiding the connecting pin. On the other hand, a portion near the end portion of the connecting pin, which is brought into contact with the engaging member, may be formed of a metal material having a rigidity lower than that of the remaining portion. Each dynode plate has the engaging member adapted to be engaging with a corresponding one of the connecting pins and projecting from a predetermined portion of a side surface thereof in parallel to the incident direction of said photoelectrons, and the predetermined portion of the dynode plates adjacent to each other do not cause the engaging members to overlap each other in the stacking direction of the dynode plates. The arrangement position of the engaging member provided to the side surface of each dynode plate and the arrangement position of a through hole formed in the base member to guide the connecting pin for individually applying a voltage to the desired dynode plate are matched with each other in the stacking direction of the dynode plates. As described above, the engaging member provided to the side surface of each dynode plate and the through hole of the connecting pin corresponding to this engaging member are matched with each other at their arrangement positions in the stacking direction of the dynode unit. Therefore, the connecting pin is not bent to reach a desired connecting portion, or indirectly connected through another wiring member. That is, these complicated steps in manufacturing the photomultiplier become unnecessary, thereby providing a structure in which a voltage is applied by a connecting pin having a minimum length for each dynode plate. In addition, the connecting pin guided to the base member is fixed at a predetermined portion to the base member by a fixing member consisting of a glass material. The fixing member has a shape tapered from the surface of the base member along the connecting pin. This is because the breakdown voltage or leakage current of this fixing portion is taken into consideration. Each dynode plate is constituted by at least two plates, each having at least one opening for forming as the dynode and integrally formed by welding such that the openings are matched with each other to function as the dynode when the two plates are overlapped. To integrally form these two plates by welding, each of the plates has at least one projecting piece for welding the corresponding two plates. The side surface of the plate is located in parallel with respect to the incident direction of the photoelectrons. The engaging member is provided to each dynode plate at the position of the corresponding connecting pin in advance. Therefore, at the time of assembling, the position of the engaging member of each dynode plate and the position of the corresponding connecting pin are matched with each other in the stacking direction of the dynode plates. A pair of guide pieces for constituting the engaging member can be connected to the corresponding connecting pin at this portion by resistance-welding or the like. The present invention will become more fully understood from consideration of a detailed description of embodiments given hereinbelow with reference to the accompanying drawings. The description and drawings are given by way of illustration only, and thus are not to be considered as limiting the present invention. In the drawings: Fig. 1 is a partially cutaway sectional view showing the entire structure of a photomultiplier embodying the present invention; Fig. 2 is a sectional view showing a typical shape of a concave portion formed in a dynode plate in the photomultiplier embodying the present invention; Fig. 3 is a sectional view showing the first shape of the concave portion as a first application of the concave portion shown in Fig. 2; Fig. 4 is a sectional view showing the second shape of the concave portion as a second application of the concave portion shown in Fig. 2; Fig. 5 is a sectional view showing the third shape of the concave portion as a third application of the concave portion shown in Fig. 2; Fig. 6 is a sectional view showing the fourth shape of the concave portion as a fourth application of the concave portion shown in Fig. 2; Fig. 7 is a sectional view showing the structure of a comparative example for explaining the effect of the present invention; Fig. 8 is a sectional view showing the structure between dynode plates, for explaining the effect of the present invention; Fig. 9 is a sectional side view showing the simple internal structure of the photomultiplier, in which a metal housing in the photomultiplier embodying the present invention is cut; Fig. 10 is a plan view showing the photomultiplier embodying the present invention shown in Figs. 1 and 9; Fig. 11 is a plan view showing the bottom surface of the photomultiplier shown in Fig. 9; Fig. 12 is an enlarged view showing the first embodiment of an engaging member provided to each dynode plate; and Fig. 13 is an enlarged view showing the second embodiment of an engaging member provided to each dynode plate. Embodiments of the present invention will be described below with reference to Figs. 1 to 13. Fig. 1 is a perspective view showing the entire structure of a photomultiplier embodying the present invention. Referring to Fig. 1, the photomultiplier is basically constituted by a photocathode 3 and an electron multiplier. The electron multiplier includes anodes (anode plate 5) and a dynode unit 60 arranged between the photocathode 3 and the anodes. The electron multiplier is mounted on a base member 4 and arranged in a housing 1 which is formed integral with the base member 4 to fabricate a vacuum container. The photocathode 3 is arranged inside the housing 1 and deposited on the surface of a light receiving plate 2 provided to the housing 1. The anodes are supported by the anode plate 5 and arranged between the dynode unit 60 and the base member 4. The dynode unit 60 is constituted by stacking a plurality of stages of dynode plates 6, for respectively supporting a plurality of dynodes 603 (Fig. 2) for receiving and cascade-multiplying photoelectrons emitted from the photocathode 3, in the incidence direction of the photoelectrons. The photomultiplier also has focusing electrodes 8 between the dynode unit 60 and the photocathode 3 for correcting orbits of the photoelectrons emitted from the photocathode 3. These focusing electrodes 8 are supported by a focusing electrode plate 7. The focusing electrode plate 7 is fixed on the electron incidence side of the dynode unit 60 through insulating members 8a and 8b. The focusing electrode plate 7 has holding springs 7a and contact terminals 7b, all of which are integrally formed with this plate 7. The holding springs 7a are in contact with the inner wall of the housing 1 to hold the arrangement position of the dynode unit 60 fixed on the focusing electrode plate 7 through the insulating members 8a and 8b. The contact terminals 7b are in contact with the photocathode 3 to equalize the potentials of the focusing electrodes 8 and the photocathode 3 and functions as springs. When the focusing electrode plate 7 has no contact terminal 7b, the housing 1 may have an inner wall thereof deposited a conductive metal for applying a predetermined voltage to the photocathode 3, and the contact portion between the housing 1 and the photocathode 3 may be rendered conductive by a predetermined conductive metal 12 to equalize the potentials of the housing 1 and the photocathode 3. Although both the contact terminals 7b and the conductive metal 12 are illustrated in Fig. 1, one structure can be selected and realized in an actual implementation. The anode is supported by the anode plate 5. A plurality of anodes may be provided to this anode plate 5, and electron passage holes through which secondary electrons pass are formed in the anode plate 5 in correspondence with positions where the secondary electrons emitted from the last-stage dynode plate of the dynode unit 60 reach. Therefore, this photomultiplier has, between the anode plate 5 and the base member 4, an inverting dynode plate 13 for supporting inverting dynodes in parallel to the anode plate 5. The inverting dynode plate 13 inverts the orbits of the secondary electrons passing through the anode plate 5 toward the anodes. The diameter of the electron incident port (dynode unit 60 side) of the electron passage hole formed in the anode plate 5 is smaller than that of the electron exit port (inverting dynode plate 13 side). The inverting dynode plate 13 has, at positions opposing the anodes, a plurality of through holes for injecting a metal vapor to form a secondary electron emitting layer on the surface of each dynode 603 of the dynode unit 60. On the other hand, the photomultiplier may have, between the inverting dynode plate 13 and the base member 4, a shield electrode plate 14 for supporting sealed electrodes in parallel to the inverting dynode plate 13. The shield electrode plate 14 inverts the orbits of the secondary electrons passing through the anode plate 5 toward the anodes. The shield electrode plate 14 has a plurality of through holes for injecting a metal vapor to form a secondary electron emitting layer on the surface of each dynode 603 of the dynode unit 60. In place of this shield electrode plate 14, a surface portion 4a of the base member 4 opposing the anode plate 5 may be used as a sealed electrode and substituted for the shield electrode plate 14. In particular, the electron multiplier comprises a dynode unit 60 constituted by stacking a plurality of stages of dynode plates 6, spaced apart from each other at predetermined intervals by the insulating members 8a and 8b in the incidence direction of the electron flow, and each dynode plate 6 is supporting a plurality of dynodes 603 for cascade-multiplying an incident electron flow, and the anode plate 5 opposing the last-stage dynode plate 6 of the dynode unit 60 through the insulating members 8a and 8b. In this electron multiplier, each dynode plate 6 has an engaging member 9 at a predetermined position of a side surface of the plate to engage with a corresponding connecting pin 11 for applying a predetermined voltage. The side surface of the dynode plate 6 is in parallel with respect to the incident direction of the photoelectrons. The engaging member 9 is constituted by a pair of guide pieces 9a and 9b for guiding the connecting pin 11. The engaging member may have a hook-like structure (engaging member 99 illustrated in Fig. 2). The shape of this engaging member is not particularly limited as long as the connecting pin 11 is received and engaged with the engaging member. On the other hand, a portion near the end portion of the connecting pin 11, which is brought into contact with the engaging member 9, may be formed of a metal material having a rigidity lower than that of the remaining portion. The engaging members 9 and 99 are respectively arranged in the side surface of the dynode plates 6 not to overlap each other in the stacking direction of the dynode plates. Through holes for guiding the connecting pins 11 are formed in a base member 4 to surround a region where the dynode unit 60 is mounted. The arrangement position of each of the engaging members 9 and 99 and the arrangement position of the corresponding through hole are matched with each other in the stacking direction of the dynode unit 60. In other words, the distal end portion of each connecting pin 11 can be inserted into the vacuum vessel by only a minimum necessary length (see Figs. 1 and 9). Therefore, the connecting pin 11 is not bent to reach a desired connecting portion, or indirectly connected through another wiring member. These complicated steps in manufacturing the photomultiplier become unnecessary, thereby providing a structure in which a voltage is applied by a connecting pin having a minimum length for each dynode plate 6. In addition, the connecting pin 11 guided to the base member 4 is fixed to the base portion 4 at a predetermined portion by a fixing member 15 (see Fig. 9) consisting of a glass material. The fixing member 15 has a shape tapered from the surface of the base member 4 along the connecting pin 11. This is because the breakdown voltage or leakage current of this fixing portion is taken into consideration. Each dynode plate 6 used is constituted by two plates 6a and 6b having openings for forming the dynodes and integrally formed by welding such that the openings are matched with each other to function as dynodes when the two plate are overlapped each other. To integrally form the two plates 6a and 6b by welding, the two plates 6a and 6b have projecting pieces 10 for welding the corresponding projecting pieces thereof at predetermined positions matching when the two plates 6a and 6b are overlapped each other. The structure of each dynode plate 6 for constituting the dynode unit 60 will be described below. Fig. 2 is a sectional view showing the shape of the dynode plate 6. Referring to Fig. 2, the dynode plate 6 has a first concave portion 601a for arranging a first insulating member 80a which is provided on a first main surface of the dynode plate 6 and partially in contact with the first concave portion 601a and a second concave portion 601b for arranging a second insulating member 80b which is provided on a second main surface of the dynode plate 6 and partially in contact with the second concave portion 601b (the second concave portion 601b communicates with the first concave portion 601 through a through hole 600). The first insulating member 80a arranged on the first concave portion 601a and the second insulating member 80b arranged on the second concave portion 601b are in contact with each other in the through hole 600. An interval between the contact portion 605a between the first concave portion 601a and the first insulating member 80a and the contact portion 605b of the second concave portion 601b and the second insulating member 80b is smaller than that (thickness of the dynode plate 6) between the first and second main surfaces of the dynode plate 6. Gaps 602a and 602b are formed between the surface of the first insulating member 80a and the main surface of the first concave portion 601a and between the second insulating member 80b and the main surface of the second concave portion 601b, respectively, to prevent discharge between the dynode plates 6. A central point 607a of the first insulating member 80a, a central point 607b of the second insulating member 80b, and a contact point 606 between the first and second insulating members 80a and 80b are aligned on the same line 604 in the stacking direction of the dynode plates 6 so that the intervals between the dynode plates 6 can be sufficiently kept. Using the spherical bodies 8a or circularly cylindrical bodies 8b are used as the first and second insulating members 80a and 80b (insulating members 8a and 8b in Fig. 1), the photomultiplier can be easily manufactured. When circularly cylindrical bodies are used, the side surfaces of the circularly cylindrical bodies are brought into contact with each other. The shape of the insulating member is not limited to this. For example, an insulating member having an elliptical or polygonal section can also be used as long as the object of the present invention can be achieved. Referring to Fig. 2, reference numeral 603 denotes a dynode. A secondary electron emitting layer containing an alkali metal is formed on the surface of this dynode. The shapes of the concave portion will be described below with reference to Figs. 3 to 6. For the sake of descriptive convenience, only the first main surface of the dynode plate 6 is disclosed in Figs. 3 to 6. The first concave portion 601a is generally constituted by a surface having a predetermined taper angle (α) with respect to the direction of thickness of the dynode plate 6, as shown in Fig. 3. This first concave portion 601a may be constituted by a plurality of surfaces having predetermined taper angles (α and β) with respect to the direction of thickness of the dynode plate 6, as shown in Fig. 4. The surface of the first concave portion 601a may be a curved surface having a predetermined curvature, as shown in Fig. 5. The curvature of the surface of the first concave portion 601a is set smaller than that of the first insulating member 80a, thereby forming the gap 602a between the surface of the first concave portion 601a and the surface of the first insulating member 80a. To obtain a stable contact state with respect to the first insulating member 80a, a surface to be brought into contact with the first insulating member 80a may be provided to the first concave portion 601a, as shown in Fig. 6. In this embodiment, a structure having a high mechanical strength against a pressure in the direction of thickness of the dynode plate 6 even compared to the above-described structures in Figs. 3 to 5 can be obtained. The detailed structure between the dynode plates 6, adjacent to each other, of the dynode unit 60 will be described below with reference to Figs. 7 and 8. Fig. 7 is a partial sectional view showing the conventional photomultiplier as a comparative example to the present invention. Fig. 8 is a partial sectional view showing the photomultiplier according to an embodiment of the present invention. In the comparative example shown in Fig. 8, the interval between the support plates 101 having no concave portion is almost the same as a distance A (between contact portions E between the support plates 101 and the insulating member 102) along the surface of the insulating member 102. On the other hand, in an embodiment of the present invention shown in Fig. 9, since concave portions are formed, a distance B (between the contact portions E between the plates 6a and 6b and the insulating member 8a) along the surface of the insulating member 8a is larger than the interval between plates 6a and 6b. Generally, discharge between the plates 6a and 6b is assumed to be caused along the surface of the insulating member 102 or 8a due to dust or the like deposited on the surface of the insulating member 102 or 8a. Therefore, as shown in this embodiment (see Fig. 8), when the concave portions are formed, the distance B along the surface of the insulating member 8a substantially increases as compared to the interval between the plates 6a and 6b, thereby preventing discharge which occurs when the insulating member 8a is inserted between the plates 6a and 6b. The detailed structure of the photomultiplier will be described with reference to Figs. 9 to 13. A photomultiplier according to this embodiment is shown in Figs. 9 to 11. In this photomultiplier, a vacuum container is constituted by a circular light receiving plate 2 for receiving incident light, a cylindrical metal tube (housing) 1 disposed along the circumference of the light receiving plate 2, and the circular stem 4 for constituting the base member. An electron multiplier for cascade-multiplying an incident electron flow is disposed in this vacuum container. This electron multiplier mainly comprises the dynode unit 60 constituted by stacking a plurality of dynode plates 6 in the incident direction of the electrons, and an anode plate 5. A photocathode 3 is provided on the lower surface of the light receiving plate 2. A focusing electrode plate 7 is disposed between the photocathode 3 and the dynode unit 60. Therefore, the electrons emitted from the photocathode 3 are focused by focusing electrodes 8 supported by the focusing electrode plate 7 and the electrons are incident on a predetermined region of the first-stage dynode plate 6 for constituting the dynode unit 60. The dynode unit 60 is constituted by stacking a plurality of stages of dynode plates 6 formed into square flat plates. A plurality of electron multiplication holes (dynodes) 603 are formed and arranged in a matrix in each dynode plate 6. The anode plate 5 and an inverting dynode plate 13 are sequentially disposed under the multilayered dynode plates 6 through insulating members. The through holes for guiding the connecting pins 11 into the vacuum container are formed in the stem 4 to surround a region where the dynode unit 60 and the like (Fig. 11) are mounted. Reference numeral 15 denotes hermetic glass serving as fixing members for fixing the connecting pins 11. Reference numeral 16 denotes a metal tip tube used to introduce an alkali metal vapor into the vacuum container or evacuate the vacuum container. After the metal tip tube 16 is used, its end portion is pressed and sealed. As shown in the enlarged view of Fig. 12, a U-shaped engaging member 9 connected to the corresponding stem pin (connecting pin 11) to be described later is integrally formed with the side surface of each dynode plate 6. In the engaging member 9, a pair of guide pieces 9a and 9b project forward. A recessed portion between the two guide pieces has almost the same diameter as that of the stem pin 11. When the stem pin 11 is pushed into this recessed portion, the stem pin 11 is fit in the engaging member 9. Each engaging member 9 is disposed to the dynode plate 6 at a position corresponding to the predetermined stem pin 11. As shown in Fig. 10, three engaging members are provided along the corresponding side surfaces of the dynode plates 6 in correspondence with the arrangement positions of the stem pins 11 (to be described later). The engaging members 9 are also provided to the above-described focusing electrode plate 7, the anode plate 5, the inverting dynode plate 13, and a shield electrode plate 14. Twelve stem pins 11 connected to external voltage terminals to apply a predetermined voltage to the dynode plates 6, the anode plate 5 and the like extend through the stem 4 serving as the base member at predetermined positions. Three stem pins 11 are arranged along each side surface of the dynode unit 60 stacked in a cubic to surround the dynode unit 60. These stem pins 11 are fixed to the stem 4 by the tapered hermetic glass 15. Each stem pin 11 has a length to reach the corresponding engaging member 9 at its distal end portion. Fig. 9 shows a state in which the four dynode plates 6 from the top are connected to the corresponding four stem pins 11. In the stem pin 11, a portion near the portion corresponding to the engaging member 9 is formed of a relatively soft material such as copper. The remaining portion is formed of a relatively rigid material such as stainless steel. With this structure, the stem pin 11 is firmly fixed to the stem 4, and at the same time, when the stem pin 11 is fit in the engaging member 9, an excess stress applied to the stem 4 can be prevented. Since the distal end portion of the stem pin 11 is slightly inclined inward, the stem pin 11 can be easily fit in the engaging member 9. The stem pins 11 which are integrally formed of the same material can be sufficiently applied. As shown in Fig. 11, the metal tip tube 16 having its end portion pressed and sealed projects from the center of the bottom portion of the stem 4. An alkali metal is introduced into the vacuum vessel or the vacuum vessel is evacuated through this metal tip tube 16, and thereafter, the metal tip tube 16 is sealed, as shown in Fig. 10. When the dynode plates 6, the anode plate 5, and the like are stacked to assemble the photomultiplier, the position of the engaging member 9 of each dynode plate 6 or the like and the position of the corresponding stem pin 11 are matched with each other in a state in which the dynode plates 6 and the like are incorporated. As a result, each engaging member 9 can be directly connected to the corresponding stem pin 11 by resistance welding or the like so that this connecting operation can be easily performed. The engaging member 9 is not formed into the conventional flat shape but a U-shape with an open end. Therefore, the stem pin 11 is firmly fit in the engaging member 9, and the distal end portion of the stem pin 11 is not needed to be bent. After the stem pin 11 is fit in the recessed portion of the engaging member 9, the distal ends of the guide pieces 9a and 9b on both the sides can be pressed to hold the stem pin 11 inside the engaging member 9. In this case, the subsequent welding operation can be facilitated. In this embodiment, the engaging member 9 is formed into a U-shaped terminal. However, the shape of the engaging member 9 is not limited to this. For example, in addition to the shape shown in Fig. 13, a C-shaped (engaging member 99 shown in Figs. 1 and 13), V-shaped, U-shaped or inverted V-shaped terminal can also be formed as long as the terminal can receive and be engaged with the stem pin 11. In addition, in this embodiment, the stem pin 11 is fit in the recessed portion (between the guide pieces 9a and 9b) of the engaging member 9. However, the stem pin 11 need not be always fit in the engaging member 9 and can be sufficiently positioned inside the engaging member 9. Further, in this embodiment, the dynode plates 6 having the engaging members 9 are disposed in the photomultiplier having the photocathode 3. However, it can also be disposed in the electron multiplier, as a matter of course. As has been described above, photomultipliers embodying the present invention have a plurality of connecting pins extending along the stacking direction of the dynode unit. The engaging member projects from the side surface of each dynode plate at the position corresponding to the connecting pin. In the photomultipliers, the position of each connecting pin and the position of the corresponding engaging member are matched with each other. Therefore, no conventional wiring member is needed. The connecting pins need not be bent. As a result, the connecting operation can be facilitated. Since resistance welding is required for only one engaging portion between each connecting pin and the corresponding engaging member, the operation efficiency of assembling can be improved. These effects are more remarkably provided when compact photomultipliers or electron multipliers are to be manufactured.

Claims: An electron multiplier comprising: an anode plate (5); a dynode unit (60) comprising a plurality of dynode plates (6) so spaced apart from each other at predetermined intervals and so supported in the stack by way of insulating members (8a, 8b) that the last dynode plate of said dynode unit (60) opposes said anode plate (5) to enable the dynode unit to effect cascade-multiplying of electrons incident thereon; and a plurality of connecting pins (11), connected to respective dynode plates (6) of the dynode unit (60) to enable desired potentials to be applied to said dynode plates; characterised in that: said dynode plates each have an engaging member (9) projecting from a predetermined portion of a side surface thereof to engage with a corresponding one of said connecting pins (11); and the positions of said predetermined portions of said dynode plates are so selected that said engaging members (9) are at different positions and do not overlap each other along the direction of the stack of dynode plates (6) in the dynode unit. An electron multiplier according to claim 1, further comprising: a base member (4) having said anode plate (5) and said dynode unit (60) mounted thereon and defining a plurality of through holes for guiding said plurality of connecting pins (11). An electron multiplier according to claim 2, wherein said anode plate (5) and said dynode unit (60) are positioned at a region on one major surface of said base member and the through holes are provided at a periphery of said region to guide said connecting pins (11) from the other major surface of said base member (4). An electron multiplier according to claim 2 or 3, wherein each of said connecting pins (11) are fixed to said base member (4) at a predetermined portion thereof by a fixing member consisting of a glass material, said fixing member having a shape tapering from said surface of said base member (4) along said connecting pins (11). An electron multiplier according to any one of claims 2 to 4, wherein the positions of said engaging members (9) and the positions of the respective through holes are arranged to match with each other so that the connecting pins (11) extend in substantially straight lines between the engaging members and the through holes. An electron multiplier according to any one of claims 2 to 5, wherein said anode plate (5) has formed therein electron passage holes through which secondary electrons pass, the holes being formed at positions where secondary electrons from a last-stage dynode plate (6) of said dynode unit (60) will be emitted, said anode plate (5) having an engaging member (9) engaged with a corresponding connecting pin (11) extending thereto from said base member (4) for applying a predetermined voltage to said anode plate (5). An electron multiplier according to claim 6, further comprising an inverting dynode plate (13) for inverting orbits of secondary electrons passing through said electron passage holes of said anode plate (5), the inverting dynode plate (13) being spaced apart from said anode plate (5) by way of an insulating member and positioned such that said anode plate (5) is held between said inverting dynode plate (13) and said last-stage dynode of said dynode unit (60), said inverting dynode plate (13) having an engaging member (9) engaged with a corresponding connecting pin (11) extending thereto from said base member (4) for applying a predetermined voltage to said inverting dynode plate (13). An electron multiplier according to claim 7, further comprising a shielding electrode plate (14) spaced apart from said inverting dynode plate (13) by way of insulating members and positioned such that said inverting dynode plate (13) is held between said anode plate (5) and said shielding electrode plate (14), said shielding electrode plate (14) having an engaging member (9) engaged with a corresponding connecting pin (11) extending thereto from said base member (4) for applying a predetermined voltage to said shielding electrode plate (14). An electron multiplier according to any preceding claim, wherein at least some of said engaging member (9) each comprise a pair of guide pieces (9a, 9b) for guiding said corresponding connecting pin. An electron multiplier according to any preceding claim, wherein the portion of said connecting pin is connected to said engaging member (9) is formed of a metal material having a rigidity lower than that of the remaining portion of said connecting pin (11). An electron multiplier according to any preceding claim, wherein said insulating member (8a, 8b) are spherical bodies or circularly cylindrical bodies. A photomultiplier having an electron multiplier as set forth in any preceding claim, and further comprising a photocathode (3) for receiving photons and emitting photoelectrons to said dynode unit (60). A photomultiplier as claimed in claim 12, as dependent on claim 2, further comprising a housing (1) having a light receiving plate (2), said photocathode (3) being deposited on an inner surface thereof, said housing (1) being secured to the base member (4). A photomultiplier according to claim 12 or 13 as dependent on claim 2 further comprising a focusing electrode plate (7) between said photocathode (3) and said dynode unit (60) for correcting orbits of incident electrons, said focusing electrode plate (7) being fixed at a first-stage dynode plate (6) of said dynode unit (60) by way of an insulating member, said focusing electrode plate (7) having an engaging member (9) engaged with a corresponding connecting pin (11) extending thereto from said base member for applying a predetermined voltage to said focusing electrode plate (7).

Inventors: ATSUMI AKIRA, HASEGAWA YUTAKA, KAWANO EIICHIRO, KUROYANAGI TOMIHIKO, KYUSHIMA HIROYUKI, MIZUIDE MASUYA, NAGURA KOJI, ATSUMI, AKIRA, HASEGAWA, YUTAKA, KAWANO, EIICHIRO, KUROYANAGI, TOMIHIKO, KYUSHIMA, HIROYUKI, MIZUIDE, MASUYA, NAGURA, KOJI
Applicants: HAMAMATSU PHOTONICS KK, HAMAMATSU PHOTONICS K.K.
Application year: 1994
Main classification: H01J43
IPC codes: H01J9, H01J43